It is recognized in the art that sewage treatment processes are generally comprised of three distinct treatment steps. Such are referred to as primary, secondary and tertiary treatments.
Current discharge requirements for treated waste water, especially from sewage treatment plants, generally call for a degree of suspended solids removal unattainable by secondary treatment technology on a predictable and uniform basis. For example, the standards currently applicable in Ohio are 8 mg/L monthly average and 12 mg/L maximum weekly average. Various types of tertiary treatment techniques and devices have been employed such as slow sand filtration, rapid gravity sand filtration, spray irrigation and polishing lagoons. Prior art patents have disclosed various tertiary treatment as well as apparatus for other treatment methods, as for example: U.S. Pat. No. 1,969,022; U.S. Pat. No. Re. 21,652; U.S. Pat. Nos. 3,774,770; 3,864,264; 3,923,649; and 3,925,205. Known prior art tertiary treatment apparatus is characterized by one or more of the following:
(A) Treatment is accomplished by mechanical-physical separation means which cause precipitation of the suspended solids as a sludge;
(B) Sludge removal is accomplished by scraping means;
(C) Sludge build-up on the filtering means is taught to be undesirable and to be avoided;
(D) Periodically the filtering means must be backwashed; and
(E) Upward flow of the to-be-treated waste is commonly sought.
The principal objectives of the present invention have been to provide a treatment process and apparatus wherein the principal treatment is accomplished by a biological filter mat dependent on solids build-up on and adjacent to biological media panels; wherein sludge may be removed with pump and air lift means and scraping means are not provided; wherein backwashing is not required; and wherein horizontal flow of the treated waste water through the panels is established.